This invention relates to a novel composite quasi-crystalline material, and more particularly to a composite quasi-crystalline material which is useful in a variety of electro-optic uses.
It is known that information contained in a video signal may be used to modulate a substantially constant source of radiation such as a collimated beam of monochromatic light which may be generated by a laser device. Such modulated light beam may then be used to generate a visible image, such as through a video display unit, or it may be used to generate a latent electrostatic image on a recording surface, etc. In such uses, the electro-optical modulator typically may contain a Pockel's cell comprising, for example, a potassium di-hydrogen phosphate crystal, whose index of refraction is periodically varied by the application of the varying voltage which represents the video signal. See, for example, U.S. Pat. Nos. 3,867,571, 3,922,485, 4,034,408, and 4,040,096. These patents all deal with a scanning device known as flying spot scanner in which video information is communicated to a scanned medium by a scanning system which utilizes a multifaceted rotating polygon for controlling the scanning cycles. Aside from the potassium di-hydrogen phosphate crystal used in the Pockel's cell disclosed in those patents, other known materials which may be used in such electro-optical modulators include LiNbO.sub.3, LiTaO.sub. 3, BSN, etc. These electro-optic modulators, which are sometimes referred to as light valves, have a wide number of uses. The property of these materials which make them useful in a device such as the Pockel's cell is their first non-linear polarization. The polarization of a material in an electric field may be described by the expression: EQU P=X.sup.(1) E+X.sup.(2) E.sup.2 +X.sup.(3) E.sup.3 + . . . EQU P=P.sup.(1) +P.sup.(2) +P.sup.(3) + . . .
in which P is the polarization of the material, E is the strength of the electric field applied, and X (Chi) is the coefficient of successive powers of the field. Since X.sup.(n) is usually about 10.sup.6 times the magnitude of X.sup.(n+1) when expressed in esus, successively higher orders of X (Chi) will only reveal themselves at progressively higher fields. With P.sup.(1) as the linear polarization, and P.sup.(2) as the first non-linear polarization, practically speaking, the coefficient X.sup.(2) is a measuure of the property of a material which may make it of use in an electro-optic device. In the electric dipole approximation, X.sup.(2) is zero in crystalline materials having a center of inversion or in non-crystalline materials with orientational averaging of molecular constituents.
The first non-linear polarization of a material in an electric field is a source of a number of important and practical optical effects. One of these effects is, as discussed above, the change in the refractive index of the material by the application of an electric field. Another effect is the conversion of light of frequency .omega. to a frequency 2.omega.. This effect is useful, for example, when an available laser has an output at a wavelength which is not particularly useful with a sensing or recording device, such as a xerographic photoreceptor, but where cutting the wavelength to one half its initial value would make the available laser useful. Thus, the output of a InGaAsP solid state laser, at 1500 nm, is not particularly useful with xerographic photoreceptors, but the conversion of this output to 750 nm would make it compatable with certain red sensitive photoreceptors. Other useful effects to be derived from non-linear polarization, such as frequency mixing, and optical rectification, as well as other effects such as pryoelectricity and piezoelectricity which can occur in media lacking inversion symmetry, will be appreciated by those skilled in the art in view of the present disclosure.
U.S. Pat. Nos. 3,938,881, 4,205,348, and 4,213,157 disclose acousto-optic modulation devices and/or laser scanning apparatus in which the composite material of the present invention also may be used.
IBM Technical Disclosure Bulletin, Vol. 14, No. 1, page 290-292 (June 1971), discloses a multi-monomolecular film materials for accoustic and optical devices, which is made of multiple layers of unimolecular film of certain organic materials supported on a substrate. The disclosure indicates that these films do not have a center of inversion, and they may be used as non-linear optical and accoustic guided wave devices.
It is also known that certain dye molecules, such as N-methyl-4'-hydroxy-4-stilbazolium betaine, a merocyanine dye molecule, has an extremely large molecular hyperpolarizibility. However, N-methyl-4'-hydroxy-4-stilbazolium betaine molecules in solution experience random orientation with the result that the first non-linear polarization of the solution as a whole is negligible. Other materials, such as 2-methyl-4-nitroaniliane exhibit large molecular hyperpolarizability as well as large values of X.sup.(2) (Chi), but it is difficult to grow good quality single crystals of such materials. The 2-methyl-4-nitroaniline is quite toxic and it does not lend itself to fabrication into optical devices.
Accordingly, it is an object of the present invention to provide a novel composite material having exceptional non-linear optical properties;
It is another object of the present invention to provide a method for making composite materials which possess non-linear optic and piezoelectric properties and which have a variety of practical uses.
These and other objects of the invention can be gathered from the following disclosure.